the log looks strange. Your rule says "Redirect" but when it fires, IIRF is *rewriting*.

To workaround the problem, I'd suggest either (a) removing the [L] on your rule, or (b) removing the [L] and replacing it with an explicit [R=3xx] modifier.

The [L] doesn't work with Redirect. It really makes sense only for rewrites. IIRF should generate a warning in the LOG file if these are present together. Yours doesn't show any such warning. Odd.

You don't say what version of IIRF you're using.
You're using an out-of-date version of IIRF. Version 1.2 is no longer maintained or updated. I recall that at one time there was a bug relating to this. But it's been fixed for a long time in IIRF v2. You should be
using IIRF v2.

the workaround I suggested above may yet work for you. But you'll encounter other problems if you don't update to the current IIRF.